Ultra high frequency oscillator



4 H. LISMAN ETAL 2,451,502

' ULTRA HIGH FREQUENCY OSCILLATOR Filed Aug. 14, 1945 FIG. 3.

INVENTOR. HENRY LISMAN EDWIN K. STODOLA ATTORNEY FIG. 1.

FIG. 2.

Patented Oct. 19,1948

UNITED STATES PATENT OFFICE ULTRA HIGH FREQUENCY OSCILLATOR Henry Lisman, Belmar, and K. Stodola; Neptune, N. J assignors to the United States of America as represented by the Secretary of War Application August 14, 1945, Serial No. 610,861 8 Claims. (Cl. 250-36) (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) 2 terminal to form a low impedance coupling at the operating frequency.

The anode tuning circuit is a resonant transmission l-ine formed by a pair of fiat metal plates 22 and 24, shorted at one end by a metal block 26 soldered on one side to plate 22 and fastened on the other side to plate '24 by means of a screw 28. Near its other end, plate 24, which is grounded, is connected to grid terminal I6 by a pronged phosphor bronze washer 30 which may be screwed or soldered to plate 24 and which has spring fingers in engagement with ring I6. By making The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to i us of any royalty thereon.

This invention relates to radio frequency electronic circuits and structures, particularly those,- adapted to operate in the 400-700 m-c. region. though not restricted thereto, it is especially adapted for use with the so-called lighthouse itype of tube, such as the GL446 or 2010 or similar "*Etypes operating as a grounded-grid triode.

low noise figure, is compact and simple in structively e c rical ength in the line, and at ture, can be easily assembled-and which can be the same time permit a relatively short physical made without complicated machine operations. length.

Another object of this invention is to provide up imp p p a 22 d p ted a novel resonant circ it, therefrom by a plate of mica or other suitable sun another object of this invention is to prodielectric material 32, is a flat plate 34 secured to vide novel means for resonating one or more of plate 32 Screws 35 and threaded into P 11 the electrode circuits of an electron tube. n insulating collar 38 p v ts s ew 34 from For a better understanding of the invention, forming a Short circuit betwe plates 22 and 34'. together with other and further objects thereof, Plat 34 is nnect d t one end to the metal reference is had to the following description taken I od te m nal 20 of tube T by screws 40 and a in connection with the accompanying drawing contact ring 42 soldered to plate 34. The other wherein like elements are indicated by like referend of plate 34 is connected t t p sitive te ence numerals and wherein: minal of a source of D.-C. plate voltage through Figure l is a schematic circuit of the invention; a feed-through condenser 44 and an R.-F. choke Figure 2is across-sectional view of an amplifier 46, which together keep the R.-F. currents out assembly incorporating the circuit in Figure 1; of the plate potential source. It will be noted that and the R.-F. plate 22 of the transmission line is not Figure 3 is a schematic circuit of a modification directly connected to D.-C. plate 34, but the caof Figure 1. pacity between said plates, indicated in dotted Referring now to Figures 1 and 2 of the drawlines at 48 in Figure 1, provides a substantially ing, the amplifier circuit and assembly is shown zero-impedance R.-F. connection from plate 22 to built around a lighthouse tube T, so called because the anode of the tube. of its stepped, cylindrical configuration, an ex- Plate 24 togetherwith a plate 48 spaced thereample of such tube being illustrated in Whinnery from form the cathode tuning line shorted at one Patent No. 2,404,261. The lower portion In is end by a metal block 50. The other end of plate of metal and constitutes the cathode terminal of 48 is soldered to a split metal sleeve 52 held in conthe tube. Portions l2 and I4 are of glass and are tact with the cathode terminal portion 10 of tube separated by a metallic ring Hi, to which the glass T by a spring ring 54. portions are fastened by glass-to-metal seals, and Filament voltage is supplied to filament prong which surrounds the actual grid of the tube. Ring of the tube through a plate 58 fastened to cathode It therefore constitutes the grid terminal of the plate 48 by screws 60 and 62, but insulated theretube. At the top of the tube is a metal cap having from by a mica separator 64 and by insulating a fiat, washer-like base portion 20 which consticollars around said screws. Filament voltage is tutes the anode terminal of the tube. As shown supplied through feed-through capacitor 66 and symbolically in Fig. 2 and structurally in the i an R.-F. choke 58, which together keep the REF. Whinnery patent, supra, cathode terminal Ill is currents out of the filament supply, thence not directly connected to the indirectly heated through plate 58, bolt 10, metal strap 12, and cathode of the tube, but is positioned so that there sleeve 14 which is in snug engagement with filais sufficient capacity between the cathode and said ment prong 58. i

It is a principal object of this invention to provide a novel R.-F. circuit and assembly which is eiiicient and stable in operation, has a relatively plates 22 and 24 of substantial area, sufiicient capacity exists therebetween to provide a rela- A resistance 18 (Figure 1) is inserted in the cathode circuit to provide a cathode-to-grid bias. Because of the relatively high capacity between the plates 48 and 58, the cathode and filament of the tube are maintained at substantially the same R.-F. potential.

The R.-F. plates 22 and 48 have semicircular ends 18 and 88, respectively, which are bent at right angles to the main body of said plates, each acting as one plate of a condenser to vary the resonant frequency of the tuned circuits, the other plates 8| and 82 being supported by, and electrically connected to the grid-ground plate 24. Plate 8| is adjustably supported by a threaded metallic block 84, and driven by a knob 88 through a simple microdrive element, consisting of a bolt 92 soldered to movable condenser plate 8I and in threaded engagement with the internal threads of a drive element 94 threaded into support 84.

By making the internal threads of element 94 finer than the external threads thereof, a relatively large rotation of knob 88 will result in a relatively small axial movement of condenser plate 88. A similar drive arrangement is used for plate 82.

There are also provided a pair of spring plates 11 and 19, each having two portions at right angles to each other, with one portion securely soldered to the grid-ground plate and the other is derived from a loop 98 coupled to an appropriate point on the plate line 22.

Figure 3 illustrates a modification of the circuit in Figure 1. In this modification, the bias resistor I8 is removed from the R.-F. circuits and connected between ground and one end of an additional fiat plate I88 supported in side-by-side relation with the filament plate 58, but insulated therefrom. The other end of line I88 is connected to the heater of the tube. Here too, the capacity between plates 48 and I88 serves to more nearly keep the cathode, heater, and filament at the same R.-F. potential. The remaining portions of the circuit in Figure 3 need not be shown since they are identical to those in Figure 1 in circuit and structure.

Design data for the above-described resonant circuits will now be given for a type GL446 tube operating at about 600 me. Due to the physical size of said tube, it is convenient to make R.-F. plate line 22 and R.-F. cathode line 48 an inch and a half in width and separated from the gridground plate by 8.2 inch.

Referring to Bureau of Standards Bulletin #74, page 235, the equation for the capacity of a parallel plate condenser with air dielectric is given by:

where S=area of one side of one plate in cm. T=separation of plates in cm.

' 4 where S= .54 A, and T==2.54 D

For a one inch length of line:

W {1 0.225- -upf.

where A=area of one side of one plate in square inches. D=separation of plates in inches W=width of plate in inches The characteristic impedance Z0 of a parallel line with air dielectric is given by:

where u=velocity of electromagnetic wave in air (Cf. Smythe, Static and Dynamic Electricity, page 472, Equation 7.)

C=capacity per inch of line in ppf.

Substituting value of 0 given above,

It is thus seen that the characteristic impedance of the line is 50.3 ohms.

The short circuit impedance of a transmission line is given by the expression:

where or =attenuation constant ohms =50.3 ohms B phase constant It may be assumed that the attenuation is negligible.

Z.,,=Z tanh jBl Zsc is reactive.

For 600 mc./s., x 4=4.93 inches To determine short circuit impedance for various lengths of line 1:

length (inches) X (ohms) ablation The valued the grid-plate capacity of the GL446 tube is 1.4 [.t/Lf. The capacity of the microdrive condenser when the circuit is tuned to 600 me. can be calculated if we make the following substitutions in the equation Adding this value to thegrid-plate capacity gives 3.2 mil.

For the grid-plate tuned circuit:

m =95 ohms Referring to the table above, it will be seen that for the line equal to approximately 3.5 inches in length, the inductive reactance is suitable so that the tank circuit may be resonated by tuning the microdrive condenser.

When tuned, the impedance of the tank circuit is exceedingly high, being limited chiefly by the 10,000 ohm plate resistance of the tube. Therefore, in order to match the output from the plate tank to a '72 ohm line, it is necessary to couple very near the shorted end of the line.

In the case of the cathode, the length of the line is calculated in the same manner as that of the R.-F. plate line. When this line is tuned its impedance will be limited by the value of the input conductance which is approximately equal to 1 /gm or approximately 200 ohms. Hence, to match 72 ohms input line it is necessary to tap on the line near to the tube.

The input R.-F. is fed to the cathode by means of a '72 ohm cable which is connected to the line by means of a suitable clip. The input position may be varied in order that the input circuit may be matched to the line. The position of the output loop may be varied in order that the line may be matched to the input of the succeeding circuit.

Although the invention has been specifically described as applied to a grounded-grid R.-F. amplifier tube, it is equally adaptable for use with conventional tubes and for use as an oscillator by providing coupling loops between the cathode and plate lines, so that sufficient feedback of the proper phase is obtained to render the circuit self-oscillating.

This completes the description of the invention. It will be seen that the structure and circuit described provide a number of advantages. The fiat plate construction of the transmission lines permits manufacture thereof by a simple stamping process and lends itself to easy assembly with the lighthouse type of triode, with a minimum of leads and, hence, a minimum of losses. It also makes possible a rigid electrical and mechanical assembly.

While therehas been described what is at present considered a preferred embodiment of the invention, it will be obvious to those skilled in the 6 What is claimed is:

1, An electronic circuit assembly comprising an electron tube having axially-spaced cathode, grid, and anode terminals arranged in the order named, three'spaced, parallel plates perpendicularly 'disposed with respect to the axis of said tube, the middle plate being substantially in the plane of the grid terminal and connected thereto, means to couple the upper and lower plates to said anode and cathode terminals, respectively, a portion of one of said plates being bent from the main body thereof, and a movable metallic plate supported by and coupled to an adjacent plate and cooperatingwith said bent portion to form a variable capacity therewith.

2. An electronic circuit assembly as set forth in claim 1, including means to provide feedback between the anode and cathode circuits, said feedback being of such phase as to render the circuit self-oscillating.

3. A radio frequency amplifier circuit assembly comprising an electron tube having axially-spaced cathode, grid, and anode terminals arranged in the order named, three spaced, parallel plates perpendicularly disposed with respect to the axis of said tube, the middle plate being substantially in the plane of the grid terminal and rigidly connected thereto, the spacing between said middle plate and the lower and upper plates being approximately that of the spacing between said grid terminal and said cathode and anode terminals, respectively, means to couple said lower and upper plates to said cathode and anode terminals, respectively, a portion of each outer plate being bent from the body thereof, a movable plate cooperating with each bent portion to form an adjustable capacitor therewith, each movable plate being supported 'by and electrically connected to said middle plate.

4. A radio frequency circuit assembly comprising an electron tube having axially-spaced cathode, grid, and anode terminals arranged in the order named, three spaced, parallel plates perpendicularly disposed with respect to the axis of said tube, the middle plate being substantially in the plane of the grid terminal and connected thereto, means to capacitatively couple said upper and lower plates to said anode and cathode terminals, respectively, said last named means comprising an additional plate supported in parallel relation to the outer surface of said upper plate and connected to said anode terminal and a source of anode potential.

5. A radio frequency circuit assembly comprising an electron tube having axially-spaced cathode, grid, and anode terminals arranged in the order named, three spaced, parallel plates perpendicularly disposed with respect to the axis of said tube, the middle plate being substantially in the plane of the grid terminal and connected thereto, means to capacitatively couple said upper and lower plates to said anode and cathode terminals, respectively, said last named means comprising an additional plate supported in capacita-r tive relation to the outer surface of said lower plate, a filament for indirectly heating the cathode of said electron tube, said additional plate being interposed in the filament heating circuit.

6. An electronic circuit assembly comprising an electron tube having an anode, grid, and cathode, a cathode terminal capacitatively coupled to said cathode structure, a resonant transmission network including an anode line and a grounded grid-line, a third line connected to said 7 cathode terminal and forming with said grid line a second resonant transmission line, a fourth line in capacitive relation to said grid line, one end of said fourth line being connected to said cathode, and the other end being connected to ground in series with a cathode biasing resistor. "11 7. In combination, an electronic circuit assembly comprising an electron tube having at least cathode, grid, and anode electrodes, each of said electrodes having separate terminals axially spaced and arranged in the named order of said electrodes, and means to tune said electrodes comprising a resonant transmission line having three spaced, parallel plates perpendicularly disposed with respect to the axis of said tube, the middle plate being substantially in the plane of said grid terminal and connected thereto, and means to capacitatively couple the upper and lower plates to said anode and cathode terminals, respectively, fourth and fifth plates respectively disposed parallel to and in capacitative relation with said upper and lower plates, said fourth plate being connected to said anode and a source of plate potential, said cathode being indirectly heated by a filament, said fifth plate being interposed in the filament heating circuit.

8. A radio frequency circuit assembly comprising an electron tube having axially-spaced cathode, grid, and anode terminals arranged in the order named, three spaced, parallel plates perpendicularly disposed with respect to the axis of REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,187,775 Fritz Jan. 23, 1940 2,228,126 Rambo Jan. 7, 1941 2,240,060 Usselman Apr. 29, 1941 2,262,365 Kinn Nov, 11, 1941 2,284,405 McArthur May 26, 1942 2,342,896 Salzberg Feb. 29, 1944 2,370,423 Roberts Feb. 27, 1945 2,404,261 Whinnery July 16, 1946 

